Without the capacity to assemble into specific structures at particular sites within a cell, proteins would not be able to build the complex organelles that carry out cell division, chemotaxis, photosynthesis or chromosome segregation. Disruption or reprogramming of processes of assembly and localization have disastrous consequences for the cell and thus the health of the organism. For example, enteropathogenic E. coli induce the rearrangement of the cytoskeleton of cells in the human gut, which is followed by vomiting and diarrhea. Listeria monocytogenes also alters the assembly of host cytoskeletal proteins in the course of infection. This organism recruits actin from the host-cell cytoplasm to form a comet-like tail which it uses to reach the host cell surface and then to infect adjacent cells. The formation of the structurally complex, multilayered coat that surrounds the B. subtilis spore provides one of the most powerful systems for the study of subcellular localization and assembly because B. subtilis is extremely amenable to genetic manipulation and morphological analysis. As a result of the application of these tools, the process of sporulation is understood in outline and studies of the assembly of spore structures have become feasible. Our long term goals are to elucidate the mechanisms that guide spore coat assembly to occur at the particular site of the spore surface and that control the formation of the coat layers. Our specific goals are to understand how two critical players in spore coat assembly, the proteins CotE and SpoIVA, control the formation of the spore coat and to identify additional proteins that are involved in spore coat morphogenesis. We will determine which regions of SpoIVA and CotE are important in coat assembly by a mutational analysis of their genes, and we will use both genetic and biochemical approaches to identify additional morphogenetic proteins. Ultimately, we hope to understand not only how the B. subtilis spore coat is formed but also to gain insight into organelle biosynthesis in a wide variety of organisms.